Obusier de 400 Modèle 1915/1916

Although the majority of combatants had heavy field artillery prior to the outbreak of the First World War, none had adequate numbers of heavy guns in service, nor had they foreseen the growing importance of heavy artillery once the Western Front stagnated and trench warfare set in. Since aircraft of the period were not yet capable of carrying large diameter bombs the burden of delivering heavy firepower fell on the artillery. Two sources of heavy artillery suitable for conversion to field use were surplus coastal defense guns and naval guns. A paradox faced artillery designers, while large caliber naval guns were common, large caliber land weapons were less common due to their weight, complexity and lack of mobility. Large caliber field guns often required extensive site preparation because the guns had to be dismantled into loads light enough to be towed by a horse team or the few traction engines of the time. Building a new gun could address the problem of taking apart, transporting and reassembling a large gun but this did not make existing heavy weapons any more mobile. Rail transport proved to be the most practical solution because the problems of heavy weight, lack of mobility and reduced setup time were addressed. ==Design==

Perhaps influenced by the success of the German's Big Bertha howitzer at the Belgian forts at Liège, Namur, and Antwerp and the French fort at Maubeuge the French Army issued a requirement for new super-heavy artillery capable of destroying deeply dug in German trenches and concrete fortifications. Existing coastal defense guns and siege mortars had proven to be only moderately effective, so the new weapon would need to be much larger. High-angle fire, projectile weight and explosive yield were the primary considerations. Since the mle 1915/1916 were classified as howitzers instead of guns the barrel did not need to be very long. The lack of spare industrial capacity or materials to produce a new weapon led to a decision to convert surplus naval gun barrels instead. Barrels There were two models of howitzer produced, the mle 1915 and the mle 1916 which were differentiated by the gun barrels used: • On July 22, 1915, at the request of the French GHQ, the Ministry of War ordered the construction of eight model 1915 howitzers and rail carriages from Saint Chamond. The barrels for these howitzers were a conversion of existing Canon de Modèle 1887 L/42 naval guns which were shortened to 25 calibers and bored out to . The barrels came from the decommissioned pre-dreadnought battleship Brennus and the two Valmy-class coastal defense ships. Six barrels were converted in 1915, with three others following in early 1916. Of the nine barrels converted, eight were rail mounted while the ninth tube served as a test piece on the Gâvres firing range. • A second order was placed in January 1917 for four more model 1916 howitzers and rail carriages with three spare barrels, which were a conversion of Canon de Modèle 1912 L/45 naval guns which were shortened to 25 calibers and bored out to 400 mm. These came from the canceled Normandie-class dreadnought battleships. Comparison Compared to the original naval gun and the modified howitzer, the mle 1915/1916 barrel is 25% shorter, the largest projectile weighs nearly twice as much, the muzzle velocity is only 60 per cent of the original and the range of the projectile is slightly shorter despite firing at greater angles of elevation. Other conversions With the success of the mle 1915/1916 in mind, the French Army requested more howitzers be built but a lack of 340 mm barrels suitable for conversion forced them to find an alternative. Surplus Canon de Modèle 1887 L/45 naval guns were converted to using the same process of shortening the barrels, boring them out and building rail carriages for them. The resulting eight howitzers and four spare barrels were called the Obusier de 370 modèle 1915 and they served alongside the Obusier de 400 Modèle 1915/1916 in both world wars. Rail carriage The railway carriage for the howitzers was called the and was used on a number of different railway guns. The howitzers were mounted on rectangular steel bases, which were suspended on two railway bogies. The rear bogie had four axles, while the front bogie had six axles. The number of axles was determined by the weight limit for European railways of per axle and 17 × 10 = . ==Battery organization==

French railway batteries usually consisted of two trains. The first was the firing train, with a locomotive, a workshop wagon, two ammunition carriages, and one or two railway guns. The second was the administrative train, with a locomotive, additional ammunition carriages, a headquarters wagon, three or more berthing carriages, a kitchen wagon and carriages for construction material and lifting equipment. In 1916 there were four batteries and in 1918 six batteries, each with two howitzers per army. Each battery was commanded by a captain of artillery, with a lieutenant and 125 men. ==First world war==

Verdun The first use of the mle 1915/1916 was during the Battle of Verdun. Two mle 1915/1916's (those of the 77th Battery of the 3rd Foot Artillery Regiment) were deployed to the south-west at Baleycourt to participate in the preparation for the French counteroffensive on October 21, 1916. It is estimated that 373 rounds of 370 mm and 400 mm were fired during this battle. Fort Douaumont was the first to be hit and then Fort Vaux. On October 23, 1916, of the fifty or so shells striking the fort, six pierced the concrete, earth, and masonry defensive works. The first exploded in the infirmary, another in the hallway, three others smashed a casemate attached to the barracks and lastly, a munitions depot was hit, triggering a fire. Explosions and toxic gases forced the German garrison to evacuate the fort, allowing the French to reoccupy it the next day. The Somme The next use of the mle 1915/1916 was during the artillery preparation of the Battle of the Somme. From June 30, 1916, they shelled the commune of Morcourt and reduced the fortified villages of Herbécourt, Estrées and Belloy-en-Santerre to ruins. ==Second World War==

All twelve howitzers were deployed to batteries of the 371° Regiment of the ALVF (Artillery lourde sur voie ferrée) in the Alsace and Lorraine area to reinforce the Maginot Line defenses. They saw no action due to a lack of targets in those sectors. After the French Armistice, eight of these were used by the Germans as 40 cm Haubitze (Eisenbahn) 752(f). Two batteries (Nos. 693 and 686) were composed of three howitzers each and were engaged during the Siege of Leningrad, the other two acted as spares. None are thought to have survived World War II. ==Ammunition==

File:Obusier de 400 en 1917.jpg|A mle 1915/1916 in travel position. File:400 mm railway howitzer 1916 AWM H04509.jpeg|A mle 1915/1916 in firing position. File:French 400 mm railway howitzer in loading position.jpeg|A mle 1915/1916 in loading position. File:111-SC-12509 - NARA - 55185167 (cropped).jpg|A mle 1915/1916 in service with US Army 53rd Coast Artillery 15 May 1918. File:German Eisenbahngeschutz Leningrad area.jpg|A 40 cm Haubitze (Eisenbahn) 752(f) near Leningrad. ==References==